The Significant New Alternatives Policy (“SNAP”) Program of the United States Environmental Protection Agency (“EPA”) is a program designed to evaluate and regulate substitutes for ozone-depleting chemicals that are being phased out under the stratospheric ozone protection provisions of the Clean Air Act (“CAA”).
The Montreal Protocol established a chlorofluorocarbon (“CFC”) phase-out. It was known that CFCs had a high ozone depleting potential and a very high global warming potential. The next generation of propellants were hydrochlorofluorocarbon (“HCFC”) compounds, which also were eventually phased out with a transition to hydrofluorocarbon (“HFC”) compounds, which were known to be non-ozone depleting, but still have a high global warming potential. Through the Kyoto Protocol and implementing EU legislation and F-Gas regulation, HFC propellants are being phased out in an attempt to achieve compositions with low global warming potential and no ozone depletion effect. One of those replacements which has been identified through the above SNAP program is the olefinic gaseous propellant, trans-1-fluoro-3,3,3-trifluoroprop-1-ene (having a trade name of Solstice® GBA) and a Chemical Abstracts' Registry No. 29118-24-9. It has been identified by its manufacturer as a drop-in replacement for 1,1,1,2-tetrafluoroethane (having a trade name of Dymel® HFC-134a). HFC-134a has a global warming potential (“GWP”) of ˜1600, which is 1600 times the global warming effect of CO2. Solstice® Gas Blowing Agent (“GBA”) is a hydrofluoroolefin propellant (“HFO”) and has an ozone depletion value of ˜0 and a GWP100 of <6. The atmospheric lifetime of Solstice® GBA is 14 days. The boiling point of Solstice® GBA is ˜19° C. (˜3° F.).
This invention is particularly suited for extending the shelf life of the reactants used to synthesize polyurethane foams blown using the gaseous propellant, trans-1-fluoro-3,3,3-trifluoroprop-1-ene (having a trade name of Solstice® 1234ze or Solstice® GBA) in polyurethane foams.
Honeywell's Solstice® Gas Blowing Agent (“GBA”) is nonflammable by ASTM E-681 and EU A11 test methods. It has a very low global warming potential (“GWP”) of <1, a low Maximum Incremental Reactivity (“MIR”), Photochemical Ozone Creation Potential (“POCP”) and is Volatile Organic Compound (“VOC”) exempt.
As used in this application, a “two-component” froth foam means that one principal foam component is supplied in one pressurized container, typically the “A” container (i.e., polymeric isocyanate, fluorocarbons, etc.) while the other principal foam component is supplied in a second pressurized container, typically the “B” container (i.e., polyols, catalysts, flame retardants, fluorocarbons, etc.) recognizing that the designations “A” and “B” may be reversed in some other countries.
As also used in this application, “shelf life” means a polyurethane foam which when subjected to accelerated aging, still results in a foam having physical properties such as foam height, gel time, density, etc. within approximately 20% of those parameters prior to accelerated aging.
As further used in this application, “accelerated aging” means storing the reactant combination and propellant at 50° C. for 12-48 days prior to reacting the “A” and “B” cylinders and spraying the polyurethane foam. Using the Arrhenius equation, this equates to 3-12 months at room temperature.
As additionally used in this application, the term “approximately” or its equivalent symbol or “about” means a value within the acceptable norms of error measurement within the polyurethane foam industry, typically within about 10 percent of the stated value.
In a two-component polyurethane foam, the “A” and “B” components form the foam or froth, when they are mixed in the nozzle. Of course, chemical reactions with moisture in the air will also occur with a catalyst-containing two-component polyurethane foam after dispensing, but the principal reaction forming the polyurethane foam occurs when the “A” and “B” components are mixed, or contact one another in the dispensing nozzle. The dispensing apparatus for a two-component polyurethane foam application has to thus address not only the metering design concerns present in a one-component dispensing apparatus, but also the mixing requirements of a two-component polyurethane foam.
Further, a “frothing” characteristic of the foam (foam assumes consistency resembling shaving cream) is enhanced by the hydrofluoroolefin (“HFO”) propellant (or similar) component, which is present in the “A” and “B” components. This HFO component is a compressed gas which exits in its liquid state under pressure and changes to its gaseous state when the liquid is dispensed into a lower pressure ambient environment, such as when the liquid components exit the gun and enter the nozzle.
While polyurethane foam is well known, the formulation varies considerably depending on application. In particular, while the polyols and isocyanates are typically kept separate in the “B” and “A” containers, other chemicals in the formulation may be placed in either container with the result that the weight or viscosity of the liquids in each container varies as well as the ratios at which the “A” and “B” components are to be mixed. In the dispensing gun applications which relate to this invention, the “A” and “B” formulations are such that the mixing ratios are generally kept equal so that the “A” and “B” containers are the same size. However, the weight, more importantly the viscosity, of the liquids in the containers invariably vary from one another. To adjust for viscosity variation between “A” and “B” chemical formulations, the “A” and “B” containers are charged (typically with an inert gas) at different pressures to achieve equal flow rates. The metering valves in a two-component gun, therefore, have to meter different liquids at different pressures at a precise ratio under varying flow rates. For this reason (among others), some dispensing guns have a design where each metering rod/valve is separately adjustable against a separate spring to compensate not only for ratio variations in different formulations but also viscosity variations between the components. The typical two-component dispensing gun in use today can be viewed as two separate one-component dispensing guns in a common housing discharging their components into a mixing chamber or nozzle. In practice, often the gun operator adjusts the ratio settings to improve gun “performance” with poor results. To counteract this adverse result, the ratio adjustment then has to be “hidden” within the gun, or the design has to be such that the ratio setting is “fixed” in the gun for specific formulations. The gun cost is increased in either event and “fixing” the ratio setting to a specific formulation prevents interchangeability of the dispensing gun.
A still further characteristic distinguishing two-component from one-component gun designs, resides in the clogging tendencies of two-component guns. Because the foam foaming reaction commences when the “A” and “B” components contact one another, it is clear that, once the gun is used, the static mixer will clog with polyurethane foam or froth formed within the mixer. This is why the nozzles, which contain the static mixer, are designed as throw away items. In practice, the foam does not instantaneously form within the nozzle upon cessation of metering to the point where the nozzles have to be discarded. Some finite amount of time must elapse. This is a function of the formulation itself, the design of the static mixer and, all things being equal, the design of the nozzle.
The dispensing gun of the present invention is particularly suited for use in two-component polyurethane foam “kits” typically sold to the building or construction trade. Typically, a small kit contains two pressurized “A” and “B” cylinders of about 7.5 inches in diameter which are pressurized anywhere between 130-250 psi, a pair of hoses for connection to the cylinders and a dispensing gun, all of which are packaged in a container constructed to house and carry the components to the site where the foam is to be applied. When the chemicals in the “A” and “B” containers are depleted, the kit is sometimes discarded or the containers can be recycled. The dispensing gun may or may not be replaced. Since the dispensing gun is included in the kit, cost considerations dictate that the dispensing gun be relatively inexpensive. Typically, the dispensing gun is made from plastic with minimal usage of machined parts.
The dispensing guns cited and to which this invention relates are additionally characterized and distinguished from other types of multi-component dispensing guns in that they are typically, “airless” and often do not contain provisions for cleaning the gun. That is, a number of dispensing or metering guns or apparatus, particularly those used in high volume foam applications, are equipped or provided with a means or mechanism to introduce air or a solvent for cleaning or clearing the passages in the gun.
While the two-component dispensing guns discussed above function in a commercially acceptable manner, it is becoming increasingly clear as the number of in-situ applications for polyurethane foam increase, that the range or the ability of the dispensing gun to function for all such applications has to be improved. As a general example, the dispensing gun design has to be able to throttle or meter a fine bead of polyurethane froth in a sealant application where the kit is sold to seal spaces around window frames, door frames, and the like in the building trade. In contrast, where the kit is sold to form insulation, an ability to meter or flow a high volume flow of chemicals is required. Still yet, in an adhesive application, liquid spray patterns of various widths and thickness are required. While the “A” and “B” components for each of these applications are specially formulated and differ from one another, one dispensing gun for all such applications involving different formulations of the chemicals is needed.
In addition to all of the above issues, the switch from the propellant HFC-134a to the propellant HFO-1234ze has created yet another opportunity for the foam industry. While HFO-1234ze performs acceptably when initially formulated and dispensed from appropriate containers, the shelf life is quite limited, typically about 1 month. However, as is typical in this industry, the shelf life of 2-component cylinders is required to be 12 months or longer. Synthesized polyurethane foams using the propellant HFO-1234ze fail when the cylinders are stored for this period of time.
The industry requires a solution in which the newly approved hydrofluoroolefinic gaseous propellants have a longer shelf life before required usage.